Ooo... now that is interesting.
I don't think tickets are available yet, but I"ll check with WNED (Buffalo PBS) to see if they might have M+G tickets later for this one.
I contacted the BPO; tickets go on sale through the BPO Box Office on August 11, 2018. They were not sure if there was going to be a M&G, but there was one the last time (2015) Celtic Woman performed a Christmas Concert with the BPO. BTW, in 2015, the M&G was conducted by the BPO, not WNED; I suspect it'll be the same this year if they do a M&G.
Got an email from the BPO this morning announcing that tickets are now on sale for the November 27, 2018 Celtic Woman
Best of Christmas Concert with the BPO at Kleinhans Music Hall, in Buffalo, NY. No word yet on a Meet & Greet.